Thermoplastic vulcanizates and processes for making the same

ABSTRACT

A process for producing thermoplastic vulcanizates, the process comprising (i) dynamically vulcanizing a rubber with a curative in a first stage, where the rubber is within a blend that includes the rubber, a thermoplastic resin, and the curative, where said step of dynamically vulcanizing occurs at a temperature at or above the melting point of the thermoplastic resin, where said step of dynamically vulcanizing employs a peroxide curative, and where said rubber includes polymeric units deriving from 5-vinyl-2-norbornene, (ii) continuing said step of dynamically vulcanizing to cause phase inversion of the blend to thereby convert the thermoplastic resin into a continuous phase, (iii) maintaining the blend at or above the melting point of the thermoplastic resin after the phase inversion, and (iv) introducing molten thermoplastic resin into the blend in a second stage, where said step of introducing molten thermoplastic resin occurs after phase inversion but before the blend is cooled to a temperature below the melting point of the thermoplastic resin.

PRIORITY CLAIM

This application is a divisional of and claims priority to U.S. patentapplication Ser. No. 10/571,333, filed Mar. 7, 2006, which is a 371National Stage Application of International Application No.PCT/US2004/30517, filed Sep. 17, 2004, which claims the benefit ofProvisional Application No. 60/503,664, filed Sep. 17, 2003, thedisclosures of all of which are herein incorporated by reference intheir entireties.

This application claims the benefit of U.S. Provisional Application No.60/503,664, filed on Sep. 17, 2003.

FIELD OF THE INVENTION

This invention is directed toward improved thermoplastic vulcanizatesand processes for making the same.

BACKGROUND OF THE INVENTION

Thermoplastic elastomers are known. They have many of the properties ofthermoset elastomers, yet they are processable as thermoplastics. Onetype of thermoplastic elastomer is a thermoplastic vulcanizate, whichmay be characterized by finely-divided rubber particles dispersed withina plastic. These rubber particles are crosslinked to promote elasticity.Thermoplastic vulcanizates are typically prepared by dynamicallyvulcanizing a rubber contained in a blend that includes the rubber and athermoplastic resin.

Some thermoplastic vulcanizates are commercially produced by dynamicallycuring the rubber with a peroxide curative. While this curing processhas the potential to produce technological useful thermoplasticvulcanizates, the use of peroxide curatives can be problematic. Inparticular, peroxide curatives can degrade the thermoplastic resin,which results in the reduction of mechanical properties.

This problem is further aggravated where harder thermoplasticvulcanizates are desired. As is known in the art, thermoplasticvulcanizates may be advantageously produced in a variety of hardnesses.The hardness can be adjusted by the level of thermoplastic resin that isincluded in the blend. Unfortunately, as the amount of thermoplasticresin is increased, the amount of peroxide curative per part of rubberthat is required to effect dynamic vulcanization must also be increasedeven though the proportionate amount of rubber is decreased. As theamount of peroxide curative is increased, the degree of thermoplasticresin degradation is likewise increased.

Attempts have been made to overcome the problem. For example, U.S. Pat.No. 4,985,502 teaches the use of less peroxide curative. Unfortunately,the use of less curative typically hinders the ability to fully cure therubber, which results in a sacrifice in engineering properties. Also,U.S. Pat. No. 5,656,693 attempts to alleviate the problem ofthermoplastic resin degradation by employing a rubber terpolymer (e.g.,ethylene-α-olefin-diene terpolymer, which may be referred to as an EADMrubber) that includes vinyl norbornene polymeric units. These rubbersare move efficiently curable with peroxides and therefore the amount ofperoxide required to achieve full cure is reduced; this results inreduced impact on the thermoplastic resin.

Other attempts to alleviate problems caused by the use of peroxidecuratives include the use of highly crystalline EADMs. As is generallyknown in the art, EADM rubbers that include a high percentage ofethylene (i.e., greater than 75 or 80 mole percent) are characterized byethylene crystallinity. These EADM rubbers are readily curable byperoxide curatives. As a result, their use in the manufacture ofthermoplastic vulcanizates have potential benefit inasmuch as lessperoxide may be needed to cure the rubber.

The use of these crystalline EADM rubber, however, limits the breadth ofthe thermoplastic vulcanizates that can be produced. For example, theamount of oil added to thermoplastic vulcanizates is deleteriouslylimited. As those skilled in the art appreciate, the addition of morethan 50-70 parts by weight oil to thermoplastic vulcanizates preparedfrom highly crystalline EADMs is extremely problematic. Thesethermoplastic vulcanizates that employ crystalline EADMs in largeramounts of oil will tend to exhibit exudation and stickiness of partsfabricated therefrom. U.S. Pat. No. 6,610,786 sets forth numerousexamples that employ highly crystalline EADMs in the manufacture ofthermoplastic vulcanizates that have little or no oil. This problemapparently exists despite the fact that this patent producesthermoplastic vulcanizates by a process where additional rubber orthermoplastic resin is added after dynamic vulcanization; thesecond-step addition of the thermoplastic resin may occur within thesame extruder used to dynamically vulcanize the original product orwithin a second extruder.

Other multiple-stage processes for the production of thermoplasticvulcanizates are likewise known as disclosed in U.S. Pat. No. 6,288,171.Thermoplastic vulcanizates have been produced by “let down” processeswhereby soft (e.g., Shore A of about 50) thermoplastic vulcanizates areproduced and pelletized. After pelletization, the pellets are blendedwith polypropylene pellets and the blend is melt mixed and extruded.This process suffers from processing inefficiencies and is believed toimpact performance properties of the thermoplastic vulcanizates. Inanother example, solid polypropylene is added in a down stream barrelduring extruder production of the thermoplastic vulcanizate by using acrammer feeder. But, the solid polypropylene is not readily misciblewith the molten thermoplastic vulcanizate in the time scale of thisprocess and therefore processing and performance shortcomings areencountered.

Because thermoplastic vulcanizates are technologically importantcompositions, there is a continued need to develop improvedthermoplastic vulcanizates that have an overall balance of improvedproperties. And, because peroxide-cured thermoplastic vulcanizates havepotential to contribute to this technology, there remains a need toimprove peroxide-cured thermoplastic vulcanizates and processes formaking the same.

SUMMARY OF THE INVENTION

In general the present invention provides a process for producingthermoplastic vulcanizates, the process comprising (i) dynamicallyvulcanizing a rubber with a curative in a first stage, where the rubberis within a blend that includes the rubber, a thermoplastic resin, andthe curative, where said step of dynamically vulcanizing occurs at atemperature at or above the melting point of the thermoplastic resin,where said step of dynamically vulcanizing employs a peroxide curative,and where said rubber includes polymeric units deriving from5-vinyl-2-norbornene, (ii) continuing said step of dynamicallyvulcanizing to cause phase inversion of the blend to thereby convert thethermoplastic resin into a continuous phase, (iii) maintaining the blendat or above the melting point of the thermoplastic resin after the phaseinversion, and (iv) introducing molten thermoplastic resin into theblend in a second stage, where said step of introducing moltenthermoplastic resin occurs after phase inversion but before the blend iscooled to a temperature below the melting point of the thermoplasticresin.

The present invention also provides a process for preparing athermoplastic vulcanizate, the process comprising (i) preparing a blendin a first stage comprising a rubber, a thermoplastic resin, and acurative, where the weight ratio of the thermoplastic resin to therubber is from 0.1:1 to 2:1, where said rubber includes polymeric unitsderiving from 5-vinyl-2-norbornene, (ii) dynamically vulcanizing therubber at a temperature above the melting temperature of thethermoplastic resin, where said step of dynamically vulcanizing employsa peroxide curative, and (iii) adding additional thermoplastic resin tothe blend in a second stage, where said step of adding additionalthermoplastic resin occurs after said step of dynamically vulcanizingcauses phase inversion of the blend, and where said step of addingadditional thermoplastic resin occurs before the blend is permitted tocool below the melting temperature of the thermoplastic resin.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The use of elastomeric copolymers including units deriving from vinylnorbornene in combination with a multiple-stage manufacturing processhas produced peroxide-cured thermoplastic vulcanizates with anunexpectedly superior overall balance of properties. The multiple-stageprocess includes a first step whereby the rubber is dynamicallyvulcanized within a blend that includes the rubber and a thermoplasticresin; and a second step whereby additional molten thermoplastic resinis added to the product of the first step. The product of the firststep, which is in its melt phase, remains in that phase between thefirst and second stages.

The blend that is dynamically vulcanized in the first stage preferablyincludes a greater volume fraction of rubber than thermoplastic resin.As a result, the thermoplastic resin is present as a discontinuousphase. As dynamic vulcanization proceeds, the viscosity of the rubberincreases and phase inversion occurs. In other words, the thermoplasticresin phase becomes continuous. In one embodiment, the rubber becomes adiscontinuous phase. In another embodiment, a co-continuous morphologyis achieved where both the rubber and the thermoplastic resin arecontinuous phases. Once phase inversion is achieved and the rubber is atleast partially cured (i.e., the thermoplastic resin becomes acontinuous phase), the first stage ends.

Dynamic vulcanization refers to a vulcanization or curing process for arubber contained in a blend that includes the rubber and at least onethermoplastic resin. The rubber is vulcanized under conditions of shearand extension at a temperature at or above the melting point of thethermoplastic resin. The rubber is thus simultaneously crosslinked anddispersed as fine particles within the thermoplastic resin matrix,although other morphologies, such as co-continuous morphologies, mayexist depending on the degree of cure, the rubber to plastic ratio, theintensity of mixing, the residence time, and the temperature.

In one embodiment, the rubber is advantageously completely or fullycured. The degree of cure can be measured by determining the amount ofrubber that is extractable from the thermoplastic vulcanizate by usingcyclohexane or boiling xylene as an extractant. These methods aredisclosed in U.S. Pat. No. 4,311,628. Preferably, the rubber has adegree of cure where less than 15 weight percent, more preferably lessthan 10 weight percent, even more preferably less than 5 weight percent,and still more preferably less than 3 weight percent of the rubber isextractable by cyclohexane at 23° C. as described in U.S. Pat. Nos.5,100,947 and 5,151,081, which are incorporated herein by reference.Alternatively, the rubber has a degree of cure such that the crosslinkdensity is preferably at least 4×10⁻⁵, more preferably at least 7×10⁻⁵,and still more preferably at least 10×10⁻⁵ moles per milliliter ofrubber. See also “Crosslink Densities and Phase Morphologies inDynamically Vulcanized TPEs,” by Ellul et al., RUBBER CHEMISTRY ANDTECHNOLOGY, Vol. 68, pp. 573-584 (1995).

Dynamic vulcanization may be effected by mixing the rubber,thermoplastic resin, and cure system at elevated temperatures inconventional mixing equipment. In one embodiment, where thethermoplastic vulcanizates are produced under low shear, the mixingequipment may include a Banbury mixer, Brabender mixer, Farrellcontinuous mixer, or the like. In another embodiment, the thermoplasticvulcanizates are produced under high shear such as described in U.S.Pat. No. 4,594,390, which is incorporated herein by reference. Highshear dynamic vulcanization can take place within extruders withkneaders or mixing elements having one or more mixing tips or flights,extruders with one or more screws, co-rotating or counter rotatingextruders or Buss kneaders. The various equipment that can be employedincludes those described in “Mixing Practices Incorporating Twin-ScrewExtruders,” by Andersen, and “Intermeshing Twin-Screw Extruders” bySakai, Chapters 20 and 21, MIXING AND COMPOUNDING OF POLYMERS: THEORYAND PRACTICE by Ica Manas-Zloczower and Zebev Tadmor, New York: Hanser,(1994), which is incorporated herein by reference.

Useful rubbers include elastomeric copolymers that include polymericunits deriving from vinyl norbornene. As is known in the art,elastomeric copolymers also preferably include units deriving fromethylene and one or more α-olefins. Useful elastomeric copolymers mayalso include units deriving from other diene monomer in addition tovinyl norbornene. In one embodiment, the elastomeric copolymers includea terpolymer having units deriving from ethylene, one or more α-olefins,and one or more diene monomers including 5-vinyl-2-norbornene. Theseethylene, α-olefin, diene terpolymers may be referred to as VNB EADMs.The α-olefins may include, but are not limited to, propylene, 1-butene,1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, or combinationsthereof. Other diene monomers that may be used in combination with the5-vinyl-2-norbornene include 5-ethylidene-2-norbornene; 1,4-hexadiene;5-methylene-2-norbornene; 1,6-octadiene; 5-methyl-1,4-hexadiene;3,7-dimethyl-1,6-octadiene; 1,3-cyclopentadiene; 1,4-cyclohexadiene; anddicyclopentadiene.

In one embodiment, the VNB EADMs include greater than 5 mole %,optionally greater than 40 mole %, optionally greater than 45 mole %,and optionally greater than 50 mole % ethylene units deriving fromethylene monomer; on the other hand, these VNB EADMs include less than75 mole %, optionally less than 65 mole %, optionally less than 60 mole%, and optionally less than 58 mole % ethylene units deriving fromethylene monomer. With respect to the diene units, in one or moreembodiments, the VNB EADMs include greater than about 0.1 mole %,optionally greater than 0.5 mole %, optionally greater than 1 mole %,optionally greater than 2 mole % diene units deriving from5-vinyl-2-norbornene monomer; on the other hand, these VNB EADMs includeless than 15 mole %, optionally less than 10 mole %, optionally lessthan 5 mole %, and optionally less than 3 mole % diene units derivingfrom 5-vinyl-2-norbornene monomer. The balance of the terpolymerincludes α-olefin units deriving from α-olefin monomer (e.g.,propylene). In other embodiments, the amount of diene present in theterpolymer may be expressed in weight percent. For example, theterpolymer may include from about 0.1 to about 5 weight percent, morepreferably from about 0.2 to about 4 weight percent, and even morepreferably from about 0.5 to about 3.0 weight percent diene unitsderiving from 5-vinyl-2-norbornene monomer. In the event that the VNBEADM includes other diene units, the overall diene content of theelastomeric copolymer will generally fall within the ranges providedabove with respect to the vinyl norbornene monomer and the overall dienecontent preferably includes greater than 30%, more preferably greaterthan 40%, more preferably greater than 50%, and even more preferablygreater than 60% units deriving from vinyl norbornene where thepercentage is based upon the total diene content.

In one embodiment, useful VNB EADMs include those described in U.S. Pat.No. 5,656,693, which is incorporated herein by reference. Theseterpolymers preferably include from about 40 to about 90 mole percent ofits polymeric units deriving from ethylene, and from about 0.2 to about5 mole percent of its polymeric units deriving from vinyl norbornene,based on the total moles of the terpolymer, with the balance comprisingunits deriving from α-olefin monomer. Other useful olefinic elastomericcopolymers are disclosed in U.S. Pat. Nos. 6,268,438, 6,288,171, and6,245,856, and International. Publication No. WO 2004/000900, which areincorporated herein by reference, with the understanding that one ormore diene units derive from 5-vinyl-2-norbornene.

The preferred VNB EADMs are characterized by a weight average molecularweight (M_(w)) that is preferably greater than 50,000, more preferablygreater than 100,000, even more preferably greater than 200,000, andstill more preferably greater than 300,000; and the weight averagemolecular weight of the preferred VNB EADMs is preferably less than1,200,000, more preferably less than 1,000,000, still more preferablyless than 900,000, and even more preferably less than 800,000. In oneembodiment, The preferred VNB EADMs have a number average molecularweight (M_(n)) that is preferably greater than 20,000, more preferablygreater than 60,000, even more preferably greater than 100,000, andstill more preferably greater than 150,000; and the number averagemolecular weight of the preferred VNB EADMs is preferably less than500,000, more preferably less than 400,000, still more preferably lessthan 300,000, and even more preferably less than 250,000.

The preferred VNB EADMs may also be characterized by having a Mooneyviscosity (ML₍₁₊₄₎ at 125° C.) per ASTM D 1646, that is greater thanabout 50, optionally greater than about 75, optionally greater thanabout 90, and optionally in the range of 100 to about 500. Where higherMooney viscosities exist, which may be useful in the practice of thisinvention, measurements may be made at higher temperatures or by usingknown “small rotor” techniques; these methods are described in WO2004/000900 which is incorporated by reference for purpose of U.S.practice. Where higher molecular weight olefinic elastomeric copolymersare employed within the thermoplastic vulcanizates of this invention,these high molecular weight polymers may be obtained in an oil-extendedform. These oil-extended copolymers typically include from about 15 toabout 100 parts by weight, per 100 parts by weight rubber, of aparaffinic oil. The Mooney viscosity of these oil-extended copolymers isfrom about 45 to about 80 and preferably from about 50 to about 70.

Useful VNB EADMs may be manufactured or synthesized by using a varietyof techniques. For example, useful techniques are disclosed in U.S. Pat.No. 5,656,693, WO 2004/000900 A1, JP 151758, and JP 210169, which areincorporated herein by reference for purposes of U.S practice. As thoseskilled in the art will appreciate, useful synthetic techniques mayinclude solution, slurry, or gas phase polymerization techniques thatemploy numerous catalyst systems such as Ziegler-Natta systems andsingle-site catalyst systems.

In one or more embodiments, the thermoplastic resins include solid,generally high molecular weight plastic materials. Exemplarythermoplastic resins include crystalline and crystallizable polyolefins,polyimides, polyesters (nylons), and fluorine-containing thermoplastics.Also, the thermoplastic resins may include copolymers of polyolefinswith styrene such as styrene-ethylene copolymer. The preferredthermoplastic resins are crystallizable polyolefins that are formed bypolymerizing ethylene or α-olefins such as propylene, 1-butene,1-hexene, 1-octene, 2-methyl-1-propene, 3-methyl-1-pentene,4-methyl-1-pentene, 5-methyl-1-hexene, and mixtures thereof. Copolymersof ethylene and propylene or ethylene or propylene with another α-olefinsuch as 1-butene, 1-hexene, 1-octene, 2-methyl-1-propene,3-methyl-1-pentene, 4-methyl-1-pentene, 5-methyl-1-hexene or mixturesthereof are also contemplated. Specifically included are the reactor,impact, and random copolymers of propylene with ethylene or the higherα-olefins, described above, or with C₁₀-C₂₀ diolefins. Comonomercontents for these propylene copolymers will typically be from 1 toabout 30% by weight of the polymer, for example, See U.S. Pat. Nos.6,268,438, 6,288,171, and 6,245,856. Blends or mixtures of 2 or morepolyolefin thermoplastics such as described herein, or with otherpolymeric modifiers, are also suitable in accordance with thisinvention. These homopolymers and copolymers may be synthesized by usingan appropriate polymerization technique known in the art such as, butnot limited to, the conventional Ziegler-Natta type polymerizations, andcatalysis employing single-site organometallic catalysts including, butnot limited to, metallocene catalysts. Useful thermoplastic resins areavailable under the tradenames PP7032™, PP1043™, PP1052™, PP1183™, andPP1042™ (ExxonMobil), ACHIEVE™ 3854, 3825, and 3904 (ExxonMobil),51SO7A™ (Lyondell), D008M™ (Aristech), and Vistamaxx PolypropyleneCopolymers™ (ExxonMobil).

These thermoplastic resins preferably have a weight average molecularweight from about 200,000 to about 2,000,000, and a number averagemolecular weight from about 80,000 to about 800,000. More preferably,these resins have a weight average molecular weight from about 300,000to about 600,000, and a number average molecular weight from about90,000 to about 150,000.

Preferably, the linear thermoplastic resins have a melt flow rate thatis less than about 10 dg/min, preferably less than about 2 dg/min, stillmore preferably less than about 1.0 dg/min, and even more preferablyless than about 0.5 dg/min.

These thermoplastic resins also preferably have a melt temperature(T_(m)) that is from about 150 to about 175° C., more preferably fromabout 155 to about 170° C., and even more preferably from about 160 toabout 170° C. The glass transition temperature (T_(g)) of these resinsis preferably from about −5 to about 10° C., more preferably from about−3 to about 5° C., and even more preferably from about 0 to about 2° C.The crystallization temperature (T_(c)) of these resins is preferably atleast about 75° C., more preferably at least about 95° C., even morepreferably at least about 100° C., and still more preferably at least105° C., with the preferred crystallization temperature ranging from105° to 110° C.

Also, these thermoplastic resins are preferably characterized by havinga heat of fusion of at least 50 J/g, preferably in excess of 75 J/g,more preferably in excess of 100 J/g, and even more preferably in excessof 120 J/g.

An especially preferred thermoplastic resin is a high-crystallinityisotactic or syndiotactic polypropylene. This polypropylene generallyhas a density of from about 0.85 to about 0.91 g/cc, with the largelyisotactic polypropylene having a density of from about 0.90 to about0.91 g/cc, and a number average molecular weight of about 120,000 and aweight average molecular weight of about 590,000. Also, high andultra-high molecular weight polypropylene that has a fractional meltflow rate are included. These polypropylene resins are characterized bya melt flow rate that is less than or equal to 10 dg/min, morepreferably less than or equal to 1.0 dg/min, and even more preferablyless than or equal to 0.5 dg/min per ASTM D-1238.

Peroxide curatives are generally selected from organic peroxides.Examples of organic peroxides include, but are not limited to,di-tert-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide,α,α-bis(tert-butylperoxy) diisopropyl benzene,2,5-dimethyl-2,5-di(t-butylperoxy)hexane (MPH),1,1-di(tert-butylperoxy)-3,3,5-trimethyl cyclohexane,n-butyl-4-4-bis(tert-butylperoxy) valerate, benzoyl peroxide, lauroylperoxide, dilauroyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3, and mixtures thereof. Also, diaryl peroxides, ketoneperoxides, peroxydicarbonates, peroxyesters, dialkyl peroxides,hydroperoxides, peroxyketals and mixtures thereof may be used.

The peroxide curatives are preferably employed in conjunction with oneor more coagent. Examples of coagents include triallylcyanurate,triallyl isocyanurate, triallyl phosphate, sulfur, N-phenylbis-maleamide, zinc diacrylate, zinc dimethacrylate, divinyl benzene,1,2 polybutadiene, trimethylol propane trimethacrylate, tetramethyleneglycol diacrylate, trifunctional acrylic ester,dipentaerythritolpentacrylate, polyfunctional acrylate, retardedcyclohexane dimethanol diacrylate ester, polyfunctional methacrylates,acrylate and methacrylate metal salts, oximer for e.g., quinone dioxime,and mixtures thereof. In order to maximize the efficiency ofperoxide/coagent crosslinking the mixing and dynamic vulcanization arepreferably carried out in a nitrogen atmosphere. Useful peroxides andtheir methods of use in dynamic vulcanization of thermoplasticvulcanizates are disclosed in U.S. Pat. No. 5,656,693, which isincorporated herein by reference.

Plasticizers, extender oils, synthetic processing oils, or a combinationthereof may also be added to the blend in the first stage. The extenderoils may include, but are not limited to, aromatic, naphthenic, andparaffinic extender oils. Exemplary synthetic processing oils arepolylinear α-olefins, polybranched α-olefins, and hydrogenatedpolyalphaolefins. The compositions of this invention may include organicesters, alkyl ethers, or combinations thereof. U.S. Pat. Nos. 5,290,886and 5,397,832 are incorporated herein in this regard. The addition ofcertain low to medium molecular weight organic esters and alkyl etheresters to the compositions of the invention dramatically lowers theT_(g) of the polyolefin and rubber components, and of the overallcomposition, and improves the low temperatures properties, particularlyflexibility and strength. These organic esters and alkyl ether estersgenerally have a molecular weight that is generally less than about10,000. It is believed that the improved effects are achieved by thepartitioning of the ester into both the polyolefin and rubber componentsof the compositions. Particularly suitable esters include monomeric andoligomeric materials having an average molecular weight below about2000, and preferably below about 600. The ester should be compatible, ormiscible, with both the polyolefin and rubber components of thecomposition; i.e. that it mix with the other components to form a singlephase. The esters found to be most suitable were either aliphatic mono-or diesters or alternatively oligomeric aliphatic esters or alkyl etheresters. Polymeric aliphatic esters and aromatic esters were found to besignificantly less effective, and phosphate esters were for the mostpart ineffective. Synthetic polyalphaolefins are also useful in loweringTg.

In certain embodiments of this invention, a polymeric processingadditive may be added in the first stage. The processing additive may bea polymeric resin that has a very high melt flow index. These polymericresins include both linear and branched molecules that have a melt flowrate that is greater than about 500 dg/min, more preferably greater thanabout 750 dg/min, even more preferably greater than about 1000 dg/min,still more preferably greater than about 1200 dg/min, and still morepreferably greater than about 1500 dg/min. The thermoplastic elastomersof the present invention may include mixtures of various branched orvarious linear polymeric processing additives, as well as mixtures ofboth linear and branched polymeric processing additives. Reference topolymeric processing additives will include both linear and branchedadditives unless otherwise specified. The preferred linear polymericprocessing additives are polypropylene homopolymers. The preferredbranched polymeric processing additives include diene-modifiedpolypropylene polymers. Thermoplastic vulcanizates that include similarprocessing additives are disclosed in U.S. Pat. No. 6,451,915, which isincorporated herein by reference.

The ingredients within the blend of the first stage may also includereinforcing and non-reinforcing fillers, antioxidants, stabilizers,rubber processing oil, lubricants, antiblocking agents, anti-staticagents, waxes, foaming agents, pigments, flame retardants and otherprocessing aids known in the rubber compounding art. Fillers andextenders that can be utilized include conventional inorganics such ascalcium carbonate, clays, silica, talc, titanium dioxide, carbon black,as well as organic and inorganic nanoscopic fillers. Fillers, such ascarbon black, may be added in combination with a carrier such aspolypropylene.

The amount of each ingredient added to the blend in the first stage mayvary, although as noted above, preferably the volume fraction of therubber is initially greater than the thermoplastic resin.

While volume fraction of the rubber is preferably greater than thethermoplastic resin (although not required), those skilled in the artappreciate that there is a minimum amount of thermoplastic resinrequired to achieve and maintain phase inversion in dynamicvulcanization, although this amount may vary based upon mixingintensity, the elasticity ratio, the viscosity ratio, interfacialtension, and the cure state. Because some of the benefits of thisinvention are achieved by adding additional thermoplastic resin afterphase invention is achieved, it is preferred that the dynamicvulcanization of the rubber within the first stage take place in thepresence of at least the minimum amount of thermoplastic resin necessaryto achieve phase inversion of the blend. Preferably, this amountincludes a thermoplastic resin to rubber weight ratio of at least 0.1:1,more preferably at least 0.2:1, even more preferably at least 0.25:1,still more preferably at least 0.3:1, and even more preferably 0.35:1.

While there is no upper limit on the amount of thermoplastic resin thatmay be present in the first stage, some of the benefits of thisinvention result from dynamically vulcanizing the rubber in the presenceof less thermoplastic resin than would otherwise be used to achievesimilar products. In other words, advantages are achieved by the step ofadding thermoplastic resin in a second stage. Accordingly, the preferredmaximum weight ratio of thermoplastic resin to rubber is less than 2:1,more preferably less than 0.8:1, even more preferably less than 0.6:1,still more preferably less than 0.5:1, more preferably less than 0.45:1,and even more preferably less than 0.4:1.

In one or more embodiments, a vulcanizing amount of curative preferablyincludes greater than 1×10⁻⁵ moles, optionally greater than 1×10⁻⁴,optionally greater than 1×10⁻³, optionally greater than or equal to0.25×10⁻², and optionally greater than or equal to 0.5×10⁻² moles per100 parts by weight rubber; on the other hand, a vulcanizing amount ofcurative preferably includes less than 4×10⁻², optionally less than3×10⁻², optionally less than 2×10⁻², optionally less than or equal to1.5×10⁻², and optionally less than or equal to 1×10⁻² moles per 100parts by weight rubber. The amount may also be expressed as a weight per100 parts by weight rubber. This amount, however, may vary depending onthe curative employed. For example, where 2,5-dimethyl-2,5 di-(t-butylperoxy)hexane is employed, the amount employed may include from about0.5 to about 12, optionally from 0.6 to about 6, and optionally fromabout 0.75 to about 3.25 parts by weight peroxide per 100 parts byweight rubber based on the weight of the active peroxide withoutdilution. In other embodiments, a vulcanizing amount of curativeincludes from about 1×10⁻⁴ moles to about 4×10⁻² moles, more preferablyfrom about 2×10⁻⁴ moles to about 3×10⁻² moles, and even more preferablyfrom about 7×10⁻⁴ moles to about 2×10⁻² moles per 100 parts by weightrubber.

The skilled artisan will be able to readily determine a sufficient oreffective amount of coagent without undue calculation orexperimentation. In preferred embodiments, the amount of coagentemployed is similar in terms of moles to the number of moles of curativeemployed. The amount of coagent may also be expressed as weight per 100parts by weight rubber. For example, where the triallylcyanurate coagentis employed, it is preferably employed in an amount from about 0.25parts by weight to about 30 parts by weight, optionally 0.5 phr to about10 parts by weight, and optionally 0.75 to 3.25 parts by weight coagentper 100 parts by weight rubber (based on the active coagent withoutdilution).

When employed as an ingredient in the first stage, the variousplasticizers, processing oils, extender oils, or synthetic processingoils may be added in amounts equal to or greater than 50 parts byweight, optionally equal to or greater than 75 parts by weight,optionally greater than or equal to 100 parts by weight, and optionallygreater than or equal to 125 parts by weight oil per 100 parts by weightrubber; on the other hand, the amount of oil employed in the first stagemay be less than 300 parts by weight, optionally less than 250 parts byweight, and optionally less than 200 parts by weight oil per 100 partsby weight rubber. The quantity of extender oil added depends upon theproperties desired, with the upper limit depending upon thecompatibility of the particular oil and blend ingredients; this limit isexceeded when excessive exuding of extender oil occurs. The amount ofester plasticizer in the composition will generally be less than about250 parts, and preferably less than about 175 parts, per 100 partsrubber.

When employed as an ingredient in the first stage, the polymericprocessing additives may be added in amounts from about 1 to about 25parts by weight, preferably from about 1.5 to about 20 parts by weight,and more preferably from about 2 to about 15 parts by weight per 100parts by weight of the rubber and thermoplastic resin combined.

When included as an ingredient in the first stage, fillers may be addedin amount from about 0 to about 250 parts by weight or preferably about10 to 200 per 100 parts by weight of rubber. The amount of carbon blackthat can be used depends, at least in part, upon the type of carbonblack and the amount of extender oil that is used. The amount ofextender oil depends, at least in part, upon the type of rubber. Highviscosity rubbers are more highly oil extendable.

Within the second stage, which begins immediately after phase inversionis achieved, additional thermoplastic resin is added to the product ofthe first stage, i.e., the phase-inverted blend or first-stagethermoplastic vulcanizate. The additional thermoplastic resin ispreferably added while it is in the molten state. In other words, theadditional thermoplastic resin is added at or above the melt temperatureof the thermoplastic resin or, in the case of an amorphous resin, at orabove the glass transition temperature of the amorphous resin.

Accordingly, additional thermoplastic resin can be added as soon asphase inversion is achieved, or it can be added later in time, so longas the product of the first stage remains in the melt. Although severalfactors such as the mixing intensity, the degree of cure, and the ratioof thermoplastic resin to rubber can impact the time at which theinversion occurs, those skilled in the art appreciate that, underconventional conditions, phase inversion of compositions where rubber isthe major volume fraction component relative to the thermoplasticcomponent will typically occur once at least about 50% to about 75% ofthe curative required to achieve a full cure of the rubber is consumed,although as noted above, full cure of the rubber is not required forpracticing this invention.

In one embodiment, the additional thermoplastic resin is added after thedesired cure is achieved. In other words, the additional thermoplasticresin is not added until the targeted cure level is achieved or thecurative added in the first stage is substantially consumed, whichgenerally refers to greater than about 90% consumption of the curativerequired to achieve full cure of the rubber.

In another embodiment, the additional thermoplastic resin is added inincremental additions. While these incremental additions are made afterphase inversion, they can be made before, after, or both before andafter full cure or complete or substantial curative consumption isachieved.

The thermoplastic resin that is added in the second stage can includeany of the thermoplastic resins employed in the first stage, althoughthe thermoplastic resin employed in each stage need not be the same.

The addition of additional thermoplastic resin advantageously providesthe ability to tailor the hardness of the overall thermoplasticvulcanizate. Accordingly, there are no thresholds or limits on theamount of thermoplastic resin that may be added in the second stage. Forexample, a sufficient amount of thermoplastic resin needed to achieve acomposition comprising up to about 400-500 parts by weight thermoplasticresin per 100 parts by weight rubber can be added during the secondstage. It is, however, preferred to add from about 10 to about 300, morepreferably from about 20 to about 200, and even more preferably fromabout 30 to about 150 parts by weight thermoplastic resin per 100 partsby weight rubber during the second stage.

In addition to the additional thermoplastic resin, other ingredients canbe added in the second stage. These additives can advantageously beadded together with or simultaneously with the additional thermoplasticresin. In other words, the molten thermoplastic resin can advantageouslyact as a carrier for these other ingredients. These ingredients includeantioxidants, processing aids, reinforcing and non-reinforcing fillers,pigments, waxes, rubber processing oil, extender oils, antiblockingagents, antistatic agents, ultraviolet stabilizers, plasticizers(including esters), foaming agents, flame retardants, scavengers,neutralization agents, and other additives known in the rubber andcompounding art.

This invention advantageously provides the ability to add filler in thefirst stage as well as in the second stage in a single-pass or one-stepprocess. Therefore, in one embodiment, filler, such as carbon black, canbe added in conjunction with the thermoplastic resin in the secondstage. It has advantageously been found that the surface properties ofthe thermoplastic vulcanizate can be tailored by employing thistechnique.

Because fillers, such as carbon black, may be introduced into thethermoplastic vulcanizate together with the thermoplastic resin duringthe second stage of the process, the amount of carbon black that mayultimately be added can vary depending upon the concentration of thecarbon black within the thermoplastic resin. Advantageously, all of thecarbon black present within the final thermoplastic vulcanizate product(e.g., 10-250 phr) can be added via the second stage, although it may bedesirable to simply add a fraction of the desired carbon black duringthe second stage.

As with the filler, the amount of oil added during the second stage canvary greatly depending on the concentration of the oil within thethermoplastic resin. Advantageously, some of the processing oil presentin the final thermoplastic vulcanizate product can be added via thesecond stage, and it may be desirable to simply add a fraction of thedesired oil during the second stage.

While the amount of oil added during the second stage can vary, theamount of oil added during the second stage may advantageously vary fromabout 5 to about 100, and more preferably form about 10 to about 50parts by weight oil per 100 parts by weight rubber.

The addition of additional thermoplastic resin within the second stagecan be achieved by employing a variety of techniques. Within the secondstage, effective melt blending of the additional thermoplastic resin ispreferably achieved. In one embodiment, the additional ingredients canbe added to the blend while the blend remains within the same mixingapparatus that was employed during the first stage. For example, where asingle twin-screw extruder is employed in a continuous operation,additional ingredients (e.g., thermoplastic resin) can be addeddownstream within the same twin screw extruder (e.g., in a downstreambarrel). This may be accomplished by employing a secondary apparatus forexample, a continuous mixer, single screw or twin screw extruder, ringextruder, or multi-screw extruder.

In another embodiment, a tandem or parallel extruder process can beemployed. In this process, two extruders are employed in sequence orparallel; the first extruder is employed as the first-stage reactorwhere dynamic vulcanization is achieved, and the second extruder isemployed as the second-stage reactor where additional moltenthermoplastic resin is added to the blend. As with the previousembodiment, the additional thermoplastic resin can be added in the meltphase by using a variety of techniques such as an extruder. Where tandemor parallel extruders are employed, the material from the first reactorremains in the melt at all times and the process is continuous.

The transition of product between the first stage and second stage iscontinuous and the product of the first stage remains in the molten ormelt phase; i.e., the product of the first stage will flow. In otherwords, the temperature of the product manufactured in the first stage isnot allowed to cool below the melting temperature or crystallizationtemperature of the thermoplastic resin prior to the addition of theadditional molten thermoplastic resin. This is true regardless of thenumber of extruders or mixers that are employed.

The product of the first stage remains in the melt until the secondstage is complete, i.e., all of the desired additional thermoplasticresin is added. After completion of the second stage, the product can becooled and handled using conventional techniques. For example, theproduct may be pelletized.

Despite the fact that the rubber may be partially or fully cured, thecompositions of this invention can be processed and reprocessed byconventional plastic processing techniques such as extrusion, injectionmolding, blow molding, and compression molding. The rubber within thesethermoplastic elastomers is usually in the form of finely-divided andwell-dispersed particles of vulcanized or cured rubber within acontinuous thermoplastic phase or matrix, although a co-continuousmorphology or a phase inversion is also possible. In those embodimentswhere the cured rubber is in the form of finely-divided andwell-dispersed particles within the thermoplastic medium, the rubberparticles typically have an average diameter that is less than 50 μm,preferably less than 30 μm, even more preferably less than 10 μm, stillmore preferably less than 5 μm and even more preferably less than 1 μm.In preferred embodiments, at least 50%, more preferably at least 60%,and even more preferably at least 75% of the particles have an averagediameter of less than 5 μm, more preferably less than 2 μm, and evenmore preferably less than 1 μm.

Preferably, compositions resulting from this multiple-stage continuousprocess will contain a sufficient amount of the elastomeric copolymer toform rubbery compositions of matter. The skilled artisan will understandthat rubbery compositions of matter are those that have ultimateelongations greater than 100 percent, and that quickly retract to 150percent or less of their original length within about 10 minutes afterbeing stretched to 200 percent of their original length and held at 200percent of their original length for about 10 minutes.

Accordingly, the resulting thermoplastic elastomers should comprise atleast about 25 percent by weight rubber. More specifically, thethermoplastic vulcanizates may include from about 15 to about 90 percentby weight, optionally from about 45 to about 80 percent by weight, andoptionally from about 60 to about 80 percent by weight or rubber, basedon the total weight of rubber and thermoplastic component combined.

The resulting thermoplastic elastomers may comprise from about 10 toabout 80 percent by weight of the thermoplastic resin based on the totalweight of the rubber and thermoplastic resin combined. Optionally, thethermoplastic elastomers comprise from about 20 to about 70 percent byweight, optionally from about 25 to a bout 40 percent by weight, andoptionally from about 30 to about 35 percent by weight of thethermoplastic resin based on the total weight of the rubber andthermoplastic resin combined.

Advantageously, the thermoplastic vulcanizates produced according tothis invention can be manufactured to be relatively hard and yet theprocess for producing them only employs that amount of curative or lessthan would conventionally be required to produce relatively softproducts. For example, thermoplastic vulcanizates having a hardness ofat least 55 Shore A, optionally at least 60 Shore A, optionally at least65 Shore A, optionally at least 70 Shore A, optionally at least 75 ShoreA, and optionally at least 40 Shore D can be produced by using thatlevel of curative that would have conventionally been employed toproduce thermoplastic vulcanizates that have a hardness of no more than55 Shore A, optionally no more than 50 Shore A, optionally no more than40 Shore A, and optionally no more than 30 Shore A.

The thermoplastic elastomers produced according to this invention areuseful for making a variety of articles such as weather seals, hoses,belts, gaskets, moldings, boots, elastic fibers, roofing sheets, foamedproducts, and like articles. They are particularly useful for makingarticles by blow molding, extrusion, injection molding, thermo-forming,calendaring, elasto-welding and compression molding techniques. Morespecifically, they are useful for making vehicle parts such as weatherseals, brake parts such as cups, coupling disks, and diaphragm cups,boots such as for constant velocity joints and rack and pinion joints,tubing, sealing gaskets, parts of hydraulically or pneumaticallyoperated apparatus, o-rings, pistons, valves, valve seats, valve guides,and other elastomeric polymer based parts or elastomeric polymerscombined with other materials such as metal/plastic combinationmaterials. Also contemplated are transmission belts including V-belts,toothed belts with truncated ribs containing fabric faced V's, groundshort fiber reinforced V's or molded gum with short fiber flocked V's.

In order to demonstrate the practice of the present invention, thefollowing examples have been prepared and tested. The examples shouldnot, however, be viewed as limiting the scope of the invention. Theclaims will serve to define the invention.

EXAMPLES Samples 1-12

Twelve thermoplastic vulcanizates were prepared by dynamicallyvulcanizing an elastomeric copolymer with a peroxide cure system.Specifically, a two-stage continuous process was employed whereinadditional polypropylene was added in the second stage. The amount ofpolypropylene added in the second stage (i.e., down-stream feed) is setforth in Table II. The polypropylene introduced in the first stage(i.e., initial feed) is likewise set forth in Table II.

The following ingredients were used in each sample, which wasmanufactured by using the procedures generally set forth in U.S. Pat.No. 4,594,390. Samples 1-3 employedpoly(ethylene-co-propylene-co-ethylene norbornene) as the elastomericcopolymer (Vistalon™ 3666), which included 75 parts by weight oil inaddition to the rubber, and Samples 4-12 employed variouspoly(ethylene-co-propylene-co-vinyl norbornene) terpolymers, whichincluded 100 parts by weight oil in addition to the rubber. Theterpolymer including units deriving from vinyl norbornene were preparedin accordance with U.S. Pat. No. 5,656,693. The specific properties ofeach elastomeric copolymer are set forth in Table I. Table II sets forththe level of curative employed and the properties of each sample.

The ingredients included 100 parts by weight of elastomeric copolymer,propylene as set forth in Table II, 131.65 parts by weight oil (totaloil including that amount added with the rubber product), 42 parts byweight clay, 3.4 parts by weight wax, 1.94 parts by weight zinc oxide,24.4 parts by weight of a carbon black-polypropylene package, 2.0 partsby weight antioxidant (Irganox 1010), 6.5 parts by weight peroxide, and6 parts by weight coagent, each based on 100 hundred parts by weightelastomeric copolymer. The peroxide was a 50% active2,5-dimethyl-2,5di-(t-butyl peroxy)hexane in oil or inert filler, thecoagent was a 50% active triallylcyanurate in inert filler, and thecarbon black package included 60% by weight polypropylene and 40% byweight carbon black. The polypropylene was characterized by having amelt flow rate of 0.7 dg/min (51SO7A Lyondell). Also provided in TableII are the results of various tests that were conducted on the samples.The amounts provided in Tables are provided in parts by weight (phr) per100 parts by weight rubber (phr) unless otherwise specified.

Even though ingredients were added as part of an initial and downstreamfeed, the overall blend remained within a melt (i.e., without changingphase) between each ingredient feed (i.e., the first and second stages).

TABLE I Diene Mooney Oil C₂ (wt. %) ML₍₁₊₄₎@125° C. (phr) (wt %)Poly(ethylene-co- 4.1 50 75 64 propylene-co-ethylene norbornene)Poly(ethylene-co- 3.0 45 100 63 propylene-co-vinyl norbornene) IPoly(ethylene-co- 0.7 52 100 63 propylene-co-vinyl norbornene) IIPoly(ethylene-co- 1.5 47 100 63 propylene-co-vinyl norbornene) III C₂ =ethylene

TABLE II Sample 1 2 3 4 5 6 Elastomeric Copolymerpoly(ethylene-co-propylene-co-ethylene 100 100 100 — — — norbornene)poly(ethylene-co-propylene-co-vinyl norbornene) I — — — 100 100 100poly(ethylene-co-propylene-co-vinyl norbornene) II — — — — — —poly(ethylene-co-propylene-co-vinyl norbornene) III — — — — — —Polypropylene I (phr) First stage 28 28 28 28 28 28 Second stage 18 1818 18 18 18 Peroxide 6.5 3.2 1.5 6.5 3.2 1.5 Coagent 6 3 1.5 6 3 1.5Properties Hardness (Shore A) 68 66 65 67 68 68 Specific Gravity 0.9970.961 0.971 0.968 0.975 0.971 Ultimate Tensile Strength (MPa) 5.33 4.153.03 6.80 7.52 6.41 Ultimate Elongation (%) 331 505 477 323 452 492 100%Modulus (MPa) 2.83 2.14 2.02 2.92 2.77 2.52 Weight Gain (%), 24 h @ 121°C. 91 147 202 84 93 112 LCR Viscosity @ 1200 s⁻¹ 66 58 60 76 73 76 ESR109 36 30 96 82 111 Tension Set (%) 13.5 18 30 10.5 14.5 18.5 RoomTemperature Cyclohexane Extractables, % 2.58, 2.61 10.07, 10.26 26.06,25.69 1.76, 1.77 4.13, 4.18 7.32, 7.09 Boiling xylene Extractables, %3.85, 5.80 15.43, 15.40 35.70, 32.94 3.31, 2.97 5.50, 3.71 8.86, 8.81Compression Set 22 h @ 100° C. (%) 33 53 76 26 34 44 Compression Set 168h @ 100° C. (%) 40 64 80 32 41 52 Sample 7 8 9 10 11 12 ElastomericCopolymer poly(ethylene-co-propylene-co-ethylene norbornene)poly(ethylene-co-propylene-co-vinyl norbornene) I — — — — — —poly(ethylene-co-propylene-co-vinyl norbornene) II 100 100 100 — — —poly(ethylene-co-propylene-co-vinyl norbornene) III — — — 100 100 100Polypropylene I (phr) First stage 28 28 28 28 28 28 Second stage 18 1818 18 18 18 Peroxide 6.5 3.2 1.5 6.5 3.2 1.5 Coagent 6 3 1.5 6 3 1.5Properties Hardness (Shore A) 68 69 68 64 65 65 Specific GravityUltimate Tensile Strength (MPa) 6.12 6.03 4.51 5.83 5.77 4.82 UltimateElongation (%) 323 456 471 321 373 438 100% Modulus (MPa) 2.76 2.56 2.282.62 2.52 2.20 Weight Gain (%), 24 h @ 121° C. 93 119 153 93 109 140 LCRViscosity @ 1200 s⁻¹ 78 73 68 81 76 72 ESR 77 68 52 97 114 130 TensionSet (%) 12.5 17 23 10 12.5 20 Room Temperature Cyclohexane Extractables,% 2.59, 2.60 6.91, 7.05 13.5, 13.25 3.23, −3.15 7.40, 7.44 13.78, 13.55Boiling xylene Extractables, % 4.94, −4.21 10.71, 10.83 21.6, 18.724.81, 4.11 9.70, 11.25 16.46, 16.96 Compression Set 22 h @ 100° C. (%)31 46 59 27 41 53 Compression Set 168 h @ 100° C. (%) 35 53 72 34 50 67

Shore hardness was determined according to ASTM D-2240. Ultimate tensilestrength, and ultimate elongation and 100% modulus were determinedaccording to ASTM D-412 at 23° C. by using an Instron testing machine.Weight gain was determined according to ASTM D-471 after 24 hours at125° C. Tension set was determined according to ASTM D-142, compressionset was determined at 25% compression according to ASTM D-395, andtoughness was determined according to ASTM D-1292.

Extrusion surface roughness (ESR) was measured as described in ChemicalSurface Treatments of Natural Rubber And EPDM Thermoplastic Elastomers:Effects on Friction and Adhesion, RUBBER CHEMISTRY AND TECHNOLOGY, Vol.67, No. 4 (1994). LCR Viscosity is measured with a Dynisco™ Capillaryrheometer at 30:1 L/D (length/diameter) at 12000 at 204° C.

Various modifications and alterations that do not depart from the scopeand spirit of this invention will become apparent to those skilled inthe art. This invention is not to be duly limited to the illustrativeembodiments set forth herein.

What is claimed is:
 1. A process for producing a thermoplasticvulcanizate, the process comprising: (i) dynamically vulcanizing arubber with a curative in a first stage, where the rubber is within ablend that includes the rubber, a propylene homopolymer, oil and thecurative, where said step of dynamically vulcanizing occurs at atemperature at or above the melting point of the propylene homopolymer,where said rubber is a terpolymer having units derived from ethylene,one or more α-olefins, and 0.1 to 3.0 mole % polymeric units derivingfrom 5-vinyl-2-norbornene, wherein said propylene homopolymer has an MFRof less than 1 g/10 min, where said curative is a peroxide curativepresent in the first stage in an amount of from 0.5 to 6 parts by weightper 100 parts by weight of the rubber, and where the weight ratio of thepropylene homopolymer to the rubber is from 0.1:1 to 0.4:1, and wherethe oil is present in the first stage in an amount of from 50 to 200parts by weight per 100 parts by weight of the rubber; (ii) continuingsaid step of dynamically vulcanizing to cause phase inversion of theblend to thereby convert the propylene homopolymer into a continuousphase; (iii) maintaining the blend at or above the melting point of thepropylene homopolymer after the phase inversion; and (iv) introducingmolten thermoplastic resin into the blend in a second stage, where thethermoplastic resin introduced into the blend in the second stage is apropylene homopolymer, propylene copolymer with ethylene, reactorpropylene copolymer, or impact propylene copolymer, where said step ofintroducing molten thermoplastic resin occurs after phase inversion butbefore the blend is cooled to a temperature below the melting point ofthe propylene homopolymer; wherein the thermoplastic vulcanizate has thefollowing properties (a)-(d): (a) Ultimate tensile strength of 5.77 to7.52 MPa, as determined in accordance with ASTM D-412 at 23° C. using anInstron testing machine; (b) Compression set of 26% to 31%, asdetermined at 25% compression, 22 hours, and 100° C. according to ASTMD-395; (c) Compression set of 32% to 35%, as determined at 25%compression, 168 hours, and 100° C. according to ASTM D-395; and (d)Tension set of 10 to 12.5%, as determined according to ASTM D-142; andfurther wherein the thermoplastic vulcanizate comprises 60 to 80 wt % ofthe rubber, based on the total weight of the rubber, the polypropylenehomopolymer from the first stage, and the thermoplastic resin from thesecond stage, and where the thermoplastic vulcanizate comprises from 30to 35 wt % of the polypropylene homopolymer from the first stage and thethermoplastic resin from the second stage, based on the total weight ofthe rubber, the polypropylene homopolymer from the first stage, and thethermoplastic resin from the second stage; provided that the totalamount of thermoplastic vulcanizate, polypropylene homopolymer from thefirst stage, and the thermoplastic resin from the second stage does notexceed 100% based on the total weight of the rubber, the polypropylenehomopolymer from the first stage, and the thermoplastic resin from thesecond stage.
 2. The process of claim 1, where the rubber is aterpolymer including polymeric units deriving from ethylene, propylene,and 5-vinyl-2-norbornene.
 3. The process of claim 1, where theterpolymer includes from about 5 to about 75 mole % units deriving fromethylene.
 4. The process of claim 1, where oil is added during thesecond stage in an amount of from about 5 to about 100 parts by weightper 100 parts of the rubber.
 5. The process of claim 1, wherein theperoxide curative includes 2,5-dimethyl-2,5-di-(t-butyl peroxy)hexane.6. A molded, extruded, or foamed article prepared with a thermoplasticvulcanizate prepared by the process of claim
 1. 7. The process of claim1, wherein the thermoplastic vulcanizate has a hardness of at least 60Shore A.
 8. The process of claim 1, wherein the first and second stagestakes place in a single mixer.
 9. The process of claim 1, wherein carbonblack filler is added in the first stage, second stage, or both stagesof the process.
 10. The process of claim 1, wherein the thermoplasticresin introduced in the second stage is a propylene homopolymer having aMFR of less than 1 g/10 min.
 11. A process for preparing a thermoplasticvulcanizate, the process comprising: (i) preparing a blend in a firststage comprising a rubber, a propylene homopolymer and a curative, wherethe weight ratio of the propylene homopolymer to the rubber is from0.1:1 to 0.4:1, where said rubber is a terpolymer having units derivedfrom ethylene, and 0.1 to 3.0 wt % polymeric units deriving from5-vinyl-2-norbornene, and wherein said propylene homopolymer has an MFRof less than 1 g/10 min, (ii) dynamically vulcanizing the rubber at atemperature above the melting temperature of the propylene homopolymer,where said step of dynamically vulcanizing employs a peroxide curativepresent in an amount of from 0.5 to 6 parts by weight per 100 parts byweight of the rubber; and (iii) adding from about 10 to 300 parts moltenthermoplastic resin per 100 parts of the rubber to the blend in a secondstage, where the thermoplastic resin introduced into the blend in thesecond stage is a propylene homopolymer, propylene copolymer withethylene, reactor propylene copolymer, or impact propylene copolymer,where said step of adding additional thermoplastic resin occurs aftersaid step of dynamically vulcanizing causes phase inversion of theblend, and where said step of adding additional thermoplastic resinoccurs before the blend is permitted to cool below the meltingtemperature of the propylene homopolymer; wherein the thermoplasticvulcanizate has the following properties (a)-(d): (a) Ultimate tensilestrength of 5.77 to 7.52 MPa, as determined in accordance with ASTMD-412 at 23° C. using an Instron testing machine; (b) Compression set of26% to 31%, as determined at 25% compression, 22 hours, and 100° C.according to ASTM D-395; (c) Compression set of 32% to 35%, asdetermined at 25% compression, 168 hours, and 100° C. according to ASTMD-395; and (d) Tension set of 10 to 12.5%, as determined according toASTM D-142; and further wherein the thermoplastic vulcanizate comprises60 to 80 wt % of the rubber, based on the total weight of the rubber,the polypropylene homopolymer from the first stage, and thethermoplastic resin from the second stage, and where the thermoplasticvulcanizate comprises from 30 to 35 wt % of the polypropylenehomopolymer from the first stage and the thermoplastic resin from thesecond stage, based on the total weight of the rubber, the polypropylenehomopolymer from the first stage, and the thermoplastic resin from thesecond stage; provided that the total amount of thermoplasticvulcanizate, polypropylene homopolymer from the first stage, and thethermoplastic resin from the second stage does not exceed 100% based onthe total weight of the rubber, the polypropylene homopolymer from thefirst stage, and the thermoplastic resin from the second stage.
 12. Theprocess of claim 11, where the process includes introducing a processingoil during the first stage in an amount of from about 50 to about 300parts by weight oil per 100 parts by weight of the rubber.
 13. Theprocess of claim 11, wherein the thermoplastic vulcanizate has ahardness of at least 60 Shore A.
 14. The process of claim 11, whereinthe first and second stages takes place in a single mixer.
 15. Theprocess of claim 11, wherein carbon black filler is added in the firststage, second stage, or both stages of the process.
 16. The process ofclaim 11, wherein the thermoplastic resin added in the second stage is apropylene homopolymer having a MFR of less than 1 g/10 min.